The invention disclosed herein pertains to an engine-transmission control system wherein the transmission ratio of the transmission can be set to determine engine speed and a fuel governor for the engine operates to effect different engine horsepower levels and a particular horsepower level for a particular engine speed, with the operating line or curve of the engine under control of the governor being along the locus of minimum fuel consumption.
When using an infinitely variable transmission with an internal combustion engine, it is desirable to control engine speed with a relationship to engine power in order to keep the engine operating on the locus of minimum fuel consumption. This desired result is sought in both hydromechanical transmissions, which have a combined mechanical and hydraulic output, as well as hydrostatic transmissions. A hydrostatic transmission is disclosed in this application while an example of a hydromechanical transmission to which the invention is applicable is shown in U.S. Pat. No. 3,733,931, owned by the assignee of this application. In order to accomplish this result, prior systems have measured both engine speed and horsepower and then translated back into an analog signal which is transmitted to the control for the hydrostatic transmission components. This varies the transmission ratio to maintain the engine on the operating line. This translation must be done with some degree of accuracy and this requires precision measurement. Examples of such prior systems are shown in U.S. Pat. No. 3,855,793, owned by the assignee of this application.